I have been reading up on this lately. I have yet to finish my research but what I have found so far suggests that you can mix the two gasses in one cylinder and use a CO2 tank and regulator with this 'beer gas' mix.
There are alot of adds out there for 'mixers' which combine the two gasses downstream of the seperate CO2 and nitrogen tanks / regulators but these tend to be expensive. The sellers of these 'mixers' try to justify their expensive equipment by showing the long term savings over the expense of mixed gas. They point out that a bottle of CO2 and a bottle of nitrogen cost less than the same volumes of gasses in the same bottle. If you are running a bar maybe this would slowly pay for itself.
As of now I am leaning towards the mixed gas in the CO2 cylinder / CO2 regulator. The biggest hurdle here is finding someone who is willing to do this. I live in a small town so its hard to find anyone to fill CO2 much less convince them that it would be o.k. for them to mix the gasses. I suggested this to one place and they thought I was trying to get them to blow up their building
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